Method for reducing acrylamide formation in thermally processed foods

ABSTRACT

A process and apparatus for a method for reducing the amount of acrylamide in thermally processed foods. This invention permits the production of foods having significantly reduced levels of acrylamide. The method relies on the manipulation of various unit operations used in the production of food products, particularly the washing and cooking unit operations. For example, the washing unit operation can be modified to provide a contacting step at an increased time and temperature, and adding components such as calcium chloride and L-cysteine to an aqueous solution used for the contacting. The cooking unit operation can be modified by dividing it into at least a higher-temperature first heating step and a lower-temperature second heating step in order to avoid the high-temperature/low-moisture conditions most favorable for acrylamide formation.

This application is a divisional of U.S. application Ser. No. 10/371,448entitled “Method for Reducing Acrylamide Formation in ThermallyProcessed Foods” filed on Feb. 21, 2003 now U.S. Pat. No. 7,393,550.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a method for reducing the amount ofacrylamide in thermally processed foods. This invention permits theproduction of foods having significantly reduced levels of acrylamide.The method relies on varying the parameters of various unit operationsto manipulate the amount of acrylamide found in the finished productwhile also maintaining product quality.

2. Description of Related Art

The chemical acrylamide has long been used in its polymer form inindustrial applications for water treatment, enhanced oil recovery,papermaking, flocculants, thickeners, ore processing and permanent-pressfabrics. Acrylamide precipitates as a white crystalline solid, isodorless, and is highly soluble in water (2155 g/L at 30° C.). Synonymsfor acrylamide include 2-propenamide, ethylene carboxamide, acrylic acidamide, vinyl amide, and propenoic acid amide. Acrylamide has a molecularmass of 71.08, a melting point of 84.5° C., and a boiling point of 125°C. at 25 mmHg.

In very recent times, a wide variety of foods have tested positive forthe presence of acrylamide monomer. Acrylamide has especially been foundprimarily in carbohydrate food products that have been heated orprocessed at high temperatures. Examples of foods that have testedpositive for acrylamide include coffee, cereals, cookies, potato chips,crackers, french-fried potatoes, breads and rolls, and fried breadedmeats. In general, relatively low contents of acrylamide have been foundin heated protein-rich foods, while relatively high contents ofacrylamide have been found in carbohydrate-rich foods, compared tonon-detectable levels in unheated and boiled foods. Reported levels ofacrylamide found in various similarly processed foods include a range of330-2,300 (μg/kg) in potato chips, a range of 300-1100 (μg/kg) in frenchfries, a range 120-180 (μg/kg) in corn chips, and levels ranging fromnot detectable up to 1400 (μg/kg) in various breakfast cereals.

It is presently believed that acrylamide is formed from the presence ofamino acids and reducing sugars. For example, it is believed that areaction between free asparagine, an amino acid commonly found in rawvegetables, and free reducing sugars accounts for the majority ofacrylamide found in fried food products. Asparagine accounts forapproximately 40% of the total free amino acids found in raw potatoes,approximately 18% of the total free amino acids found in high proteinrye, and approximately 14% of the total free amino acids found in wheat.

The formation of acrylamide from amino acids other than asparagine ispossible, but it has not yet been confirmed to any degree of certainty.For example, some acrylamide formation has been reported from testingglutamine, methionine, cysteine, and aspartic acid as precursors. Thesefindings are difficult to confirm, however, due to potential asparagineimpurities in stock amino acids. Nonetheless, asparagine has beenidentified as the amino acid precursor most responsible for theformation of acrylamide.

Since acrylamide in foods is a recently discovered phenomenon, its exactmechanism of formation has not been confirmed. However, it is nowbelieved that the most likely route for acrylamide formation involves aMaillard reaction. The Maillard reaction has long been recognized infood chemistry as one of the most important chemical reactions in foodprocessing and can affect flavor, color, and the nutritional value ofthe food. The Maillard reaction requires heat, moisture, reducingsugars, and amino acids.

The Maillard reaction involves a series of complex reactions withnumerous intermediates, but can be generally described as involvingthree steps. The first step of the Maillard reaction involves thecombination of a free amino group (from free amino acids and/orproteins) with a reducing sugar (such as glucose) to form Amadori orHeyns rearrangement products. The second step involves degradation ofthe Amadori or Heyns rearrangement products via different alternativeroutes involving deoxyosones, fission, or Strecker degradation. Acomplex series of reactions including dehydration, elimination,cyclization, fission, and fragmentation result in a pool of flavorintermediates and flavor compounds. The third step of the Maillardreaction is characterized by the formation of brown nitrogenous polymersand co-polymers. Using the Maillard reaction as the likely route for theformation of acrylamide, FIG. 1 illustrates a simplification ofsuspected pathways for the formation of acrylamide starting withasparagine and glucose.

Acrylamide has not been determined to be detrimental to humans, but itspresence in food products, especially at elevated levels, isundesirable. As noted previously, relatively higher concentrations ofacrylamide are found in food products that have been heated or thermallyprocessed. The reduction of acrylamide in such food products could beaccomplished by reducing or eliminating the precursor compounds thatform acrylamide, inhibiting the formation of acrylamide during theprocessing of the food, breaking down or reacting the acylamide monomeronce formed in the food, or removing acrylamide from the product priorto consumption. Understandably, each food product presents uniquechallenges for accomplishing any of the above options. For example,foods that are sliced and cooked as coherent pieces may not be readilymixed with various additives without physically destroying the cellstructures that give the food products their unique characteristics uponcooking. Other processing requirements for specific food products maylikewise make acrylamide reduction strategies incompatible or extremelydifficult.

By way of example, FIG. 2 illustrates well known prior art methods formaking fried potato chips from raw potato stock. The raw potatoes, whichcontain about 80% or more water by weight, first proceed to a peelingstep 21. After the skins are peeled from the raw potatoes, the potatoesare then transported to a slicing step 22. The thickness of each potatoslice at the slicing step 22 is dependent on the desired the thicknessof the final product. An example in the prior art involves slicing thepotatoes to a thickness of about 0.04 to about 0.08 inches. These slicesare then transported to a washing step 23, wherein the surface starch oneach slice is removed with water. The washed potato slices are thentransported to a cooking step 24. This cooking step 24 typicallyinvolves frying the slices in a continuous fryer at, for example, about171° C. to about 182° C. (340-360° F.) for approximately two to threeminutes. The cooking step generally reduces the moisture level of thechip to less than 2% by weight. For example, a typical fried potato chipexits the fryer with approximately 1-2% moisture by weight. The cookedpotato chips are then transported to a seasoning step 25, whereseasonings are applied in a rotation drum. Finally, the seasoned chipsproceed to a packaging step 26. This packaging step 26 usually involvesfeeding the seasoned chips to one or more weighers which then directchips to one or more vertical form, fill, and seal machines forpackaging in a flexible package. Once packaged, the product goes intodistribution and is purchased by a consumer.

Minor adjustments in a number of the potato chip processing stepsdescribed above can result in significant changes in the characteristicsof the final product. For example, an extended residence time of theslices in water at the washing step 23 can result in leaching compoundsfrom the slices that provide the end product with its potato flavor,color and texture. Increased residence times or heating temperatures atthe cooking step 24 can result in an increase in the Maillard browninglevels in the chip, as well as a lower moisture content. If it isdesirable to incorporate ingredients into the potato slices prior tofrying, it may be necessary to establish mechanisms that provide for theabsorption of the added ingredients into the interior portions of theslices without disrupting the cellular structure of the chip or leachingbeneficial compounds from the slice.

By way of another example of heated food products that represent uniquechallenges to reducing acrylamide levels in the final products, snackscan also be made as a fabricated snack. The term “fabricated snack”means a snack food that uses as its starting ingredient something otherthan the original and unaltered starchy starting material. For example,fabricated snacks include fabricated potato chips that use a dehydratedpotato product as a starting material and corn chips which use a masaflour as its starting material. It is noted here that the dehydratedpotato product can be potato flour, potato flakes, potato granules, orany other form in which dehydrated potatoes exist. When any of theseterms are used in this application, it is understood that all of thesevariations are included.

Referring back to FIG. 2, a fabricated potato chip does not require thepeeling step 21, the slicing step 22, or the washing step 23. Instead,fabricated potato chips start with a dehydrated potato product such aspotato flakes. The dehydrated potato product is mixed with water andother minor ingredients to form a dough. This dough is then sheeted andcut before proceeding to a cooking step. The cooking step may involvefrying or baking. The chips then proceed to a seasoning step and apackaging step. The mixing of the potato dough generally lends itself tothe easy addition of other ingredients. Conversely, the addition of suchingredients to a raw food product, such as potato slices, requires thata mechanism be found to allow for the penetration of ingredients intothe cellular structure of the product. However, the addition of anyingredients in the mixing step must be done with the consideration thatthe ingredients may adversely affect the sheeting characteristics of thedough as well as the final chip characteristics.

It would be desirable to develop one or more methods of reducing thelevel of acrylamide in the end product of heated or thermally processedfoods. Ideally, such a process should substantially reduce or eliminatethe acrylamide in the end product without adversely affecting thequality and characteristics of the end product. Further, the methodshould be easy to implement and, preferably, add little or no cost tothe overall process.

SUMMARY OF THE INVENTION

The present invention is a method for reducing the amount of acrylamidein thermally processed food products. According to one embodiment, themethod comprises providing a continuous feed of peeled and sliced rawpotatoes and contacting the continuous feed of raw potato slices with anaqueous solution at about 60° C. (140° F.) for about five minutes toreduce the amount of acrylamide precursor in the raw potato slices.According to another embodiment, the method comprises providing acontinuous feed of peeled and sliced raw potatoes, par-frying the rawpotato slices at about 171° C. to about 182° C. (340-360° F.) until themoisture content is reduced to about 3-10% moisture by weight, thenoven-drying the par-fried slices at less than about 120° C. (250° F.)until the moisture content is further reduced to about 1-2% moisture byweight. According to another embodiment, the method comprises contactinga continuous feed of raw potato slices with an aqueous solution at about60° C. (140° F.), followed by par-frying the raw contacted potato slicesat about 171° C. to about 182° C. (340-360° F.) until the moisturecontent is reduced to about 3-10% moisture by weight, then oven-dryingthe par-fried slices at less than about 120° C. (250° F.) until themoisture content is further reduced to about 1-2% moisture by weight.Other embodiments involve different combinations of various methods forcontacting and cooking a continuous feed of peeled and sliced potatoesas well as the manipulation of various other unit operations. Bymanipulating these unit operations, one can avoid creating theconditions most favorable for acrylamide formation and thereby reduceacrylamide formation in the thermally processed food product.

For example, the washing step of a typical potato-chip-making processcan be manipulated to comprise a contacting step where the potato slicesare contacted with an aqueous solution. The contact time and temperaturecan be increased and manipulated, and one or more ingredients can beadded to the aqueous solution. The cooking step can be manipulated bydividing it into a higher-temperature first heating step and alower-temperature second heating step. The higher-temperature firstheating step can comprise atmospheric frying, vacuum frying, pressurefrying, microwave-assisted frying, or baking, and other means known inthe art. The second heating step can comprise vacuum frying, lowtemperature oven drying, vacuum oven drying, or any method of cookingthat maintains cooking temperatures required by the second heating step.Other methods for manipulating the contacting and cooking unitoperations to reduce acrylamide formation are possible.

The above, as well as additional features and advantages of theinvention will become apparent in the following written detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asa preferred mode of use, further objectives and advantages thereof, willbe best understood by reference to the following detailed description ofillustrative embodiments when read in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a schematic of suspected chemical pathways for acrylamideformation;

FIG. 2 is a schematic of prior art potato chip processing steps;

FIG. 3 is a graph showing, on the y-axis in parts per billion (“ppb”),acrylamide concentrations of potato test samples that were fried aftercontacting in various ways described along the x-axis, as well as thefinal moisture content by weight;

FIG. 4 is a graph comparing the original results from FIG. 3 with theFIG. 3 results after normalization to a moisture content of 1.32% byweight;

FIG. 5 is a graph showing the relationship between acrylamideconcentration and final fried product moisture wherein the acrylamideconcentration in ppb is on the y-axis, and the moisture content inweight percent is on the x-axis;

FIG. 6 is a graph showing the relationship between acrylamideconcentration and final baked product moisture wherein the acrylamideconcentration in ppb is on the y-axis, and the moisture content inweight percent is on the x-axis;

FIG. 7 a is a graph showing the acrylamide concentrations in potato testsamples that were par-fried and then oven-dried at about 120° C. (250°F.) after various methods of contacting, wherein acrylamideconcentrations are shown on the y-axis in ppb, and the various contactmethods are described on the x-axis;

FIG. 7 b is a graph showing the last six data points of FIG. 7 a on anarrower acrylamide concentration scale;

FIG. 8 is a graph showing the data from FIG. 7 a after normalizing thepar-fry data to a moisture level of 3.13% by weight and normalizing theoven-dry data to a moisture level of 1.25% by weight;

FIG. 9 is a graph showing on the y-axis in ppb: 1) the acrylamide levelsof potato test samples that were contacted in the various ways shown onthe x-axis, then par-fried at about 178° C. (353° F.), and 2) theacrylamide levels of those same potato test samples after oven-drying atabout 176° C. (350° F.), normalized to a moisture level of 0.76% byweight;

FIG. 10 is a chart showing the operating conditions and results of anexperiment in which a control sample of potato slices was atmosphericfried to 1.4% moisture by weight, and a test sample was atmosphericfried to 2.5% moisture by weight, then oven-dried to 1.4% moisture byweight;

FIG. 11 is a chart showing the operating conditions and results ofseveral experiments in which a control sample of potato slices wasatmospheric fried to about 0.8% moisture by weight, and four testsamples were atmospheric par-fried to about 3-10% moisture by weight,then low-temperature vacuum fried to below 1% moisture by weight; and

FIG. 12 is a chart showing the operating conditions and results of sevenexperiments in which four test samples were atmospheric fried in oilwith initial temperatures ranging from 20 about 165 to about 180° C.(329-356° F.) for about 3-4 minutes, and three test samples werelow-temperature vacuum fried for about 4-10 minutes at temperaturesranging from about 100 to about 140° C. (212-284° F.) and pressuresranging from 50-100 millibars.

DETAILED DESCRIPTION OF THE INVENTION

The formation of acrylamide in thermally processed foods requires asource of carbon and a source of nitrogen. It is hypothesized thatcarbon is provided by a carbohydrate source and nitrogen is provided bya protein source or amino acid source. Many plant-derived foodingredients such as rice, wheat, corn, barley, soy, potato and oatscontain asparagine and are primarily carbohydrates having minor aminoacid components. Typically, such food ingredients have a small aminoacid pool, which contains other amino acids in addition to asparagine.

By “thermally processed” is meant food or food ingredients whereincomponents of the food, such as a mixture of food ingredients, areheated at temperatures of at least 80° C. Preferably, the thermalprocessing of the food or food ingredients takes place at temperaturesbetween about 100° C. and about 205° C. The food ingredient may beseparately processed at elevated temperature prior to the formation ofthe final food product. An example of a thermally processed foodingredient is potato flakes, which is formed from raw potatoes in aprocess that exposes the potato to temperatures as high as 170° C.Examples of other thermally processed food ingredients include processedoats, par-boiled and dried rice, cooked soy products, corn masa, roastedcoffee beans and roasted cacao beans. Alternatively, raw foodingredients can be used in the preparation of the final food productwherein the production of the final food product includes a thermalheating step. One example of raw material processing wherein the finalfood product results from a thermal heating step is the manufacture ofpotato chips from raw potato slices by the step of frying at atemperature of from about 100° C. to about 205° C. or the production offrench fries fried at similar temperatures.

In accordance with the present invention, however, a significantformation of acrylamide has been found to occur when the amino acidasparagine is heated in the presence of a reducing sugar. Heating otheramino acids such as lysine and alanine in the presence of a reducingsugar such as glucose does not lead to the formation of acrylamide. But,surprisingly, the addition of other amino acids to the asparagine-sugarmixture can increase or decrease the amount of acrylamide formed.

Having established the rapid formation of acrylamide when asparagine isheated in the presence of a reducing sugar, a reduction of acrylamide inthermally processed foods can be achieved by inactivating theasparagine. By “inactivating” is meant removing asparagine from the foodor rendering asparagine non-reactive along the acrylamide formationroute by means of conversion or binding to another chemical thatinterferes with the formation of acrylamide from asparagine.

Investigations into the effects of the various unit operations orprocessing steps on the formation of acrylamide in finished foodproducts have lead to interesting results. These results demonstrate anability to modify one or more unit operations in any given prior artprocess for making a food product so that the resulting cooked foodproduct has a reduced concentration of acrylamide. By “reducedconcentration of acrylamide” is meant a concentration of acrylamide thatis lower than the concentration that would have formed during anunmodified prior art process for cooking the particular food product inquestion. The terms “reduced concentration of acrylamide,” “reducedacrylamide concentration,” and “reduced acrylamide level” are all usedinterchangeably in this application. For the purpose of thisapplication, “unit operations” means a definable segment of an overallmethod for producing a food product. For example, referring to FIG. 2,each one of the potato chip processing steps (the peeling step 21, theslicing step 22, the washing step 23, the cooking step 24, the seasoningstep 25, and the packaging step 26) is considered a separate unitoperation with regard to the overall process of producing a potato chipfood product.

A first example of the manipulation of a unit operation involves thewashing step 23 (illustrated in FIG. 2) of potato chips produced byslicing raw potato stock. The prior art method of washing slicesinvolves rinsing the chips with water at room temperature. The averageresidence time of each chip in this water rinse in the prior art istypically less than about 60 seconds, depending on the equipment used.

FIG. 3 illustrates how the chip washing unit operation can bemanipulated such that acrylamide levels in the finished chip product canbe adjusted. According to the present invention, the washing step 23 canbe manipulated to comprise a contacting step, where a continuous feed ofpotato slices is contacted with an aqueous solution for residence timesand at temperatures that differ from those used in the prior art washingstep. FIG. 3 is a chart showing on the left (from the viewer'sperspective) vertical or y-axis, the amount of acrylamide (“AA”) inparts per billion (“ppb”) found in the finished potato chip product. Theright vertical or y-axis of the graph in FIG. 3 shows the percentmoisture by weight in the finished chip product. The acrylamide level ischarted on the graph by the vertical bars, while the percent moisturelevel is charted by the line plot. The horizontal or x-axis of the chartshown in FIG. 3 lists various processing parameter changes made to thewashing unit operations of a potato chip manufacturing process. Thecooking time and temperature were identical for all product runsreflected in FIG. 3. Specifically, each sample was fried at about 178°C. (353° F.) for about 120-140 seconds. Consequently, the moisturelevels of the end product tended to vary.

By way of comparison to the results shown in FIG. 3, the prior artwashing step described above, using chip-stock potatoes sliced to athickness of 0.05 inches and fried at about 178° C. (353° F.) for about120-140 seconds, results in a finished product having an acrylamidelevel of about 300-500 ppb (which can be higher depending on glucosecontent and other potato stock variable) and a final moisture level byweight of about 1.4%. This prior art result is quite similar to thefirst data point 31 found on the chart shown in FIG. 3, which representsthe base data point and involves a washing step with a water residencetime for the potato slices of two to three minutes. Maintaining allother parameters in the overall processing of the potato chip, thisminor change in the washing unit operations results in no noticeablechange in the acrylamide level (approximately 330 ppb) or the moisturelevel of the finished product (approximately 1.35%), as compared to aproduct finished according to the prior art washing step.

The next data point 32 shown on the graph in FIG. 3 reflects a change inthe washing step that comprises contacting the potato slices with wateras the aqueous solution, increasing the contact time of the aqueoussolution with the potato slices to ten minutes, and increasing thetemperature of the aqueous solution from ambient or room temperature toabout 38° C. (100° F.). This adjustment resulted in a decrease of theacrylamide in the finished product to approximately 210 ppb and areduction in the moisture level of the finished product to less than 1%by weight. Interestingly, the third data point 33 reflects thatincreasing the aqueous solution (again, water) temperature to about 54°C. (130° F.) with an average contact time of five minutes did not resultin appreciable reduction in acrylamide levels in the finished product.By contrast, the fourth data point 34 demonstrates an appreciablereduction in acrylamide levels in the final product (below 100 ppb) whenthe washing unit operation involves a contacting step providing oneminute contact time with an aqueous solution comprising water at atemperature of about 82° C. (180° F.). However, the moisture level ofthe end-product chip was nearly 1.8%. The fifth data point 35 reflectsthat using a 1% L-Cysteine solution as the aqueous solution, at ambienttemperatures for fifteen minutes, reduces the acrylamide level in thefinal product to less than 250 ppb.

In the graph illustrated in FIG. 4, the experiment results shown in FIG.3 (the first of each pair of vertical bars) are normalized to depict theacrylamide levels that could be expected if the test samples were friedto the same standardized moisture level (the second of each pair ofvertical bars). By assuming that the percent change in acrylamide levelis inversely proportional to the percent change in the moisture levelwhen moisture levels are low, the results of the test data shown in FIG.3 can be normalized by multiplying the actual acrylamide levels by thepercent change in the moisture levels required to reach the finalmoisture level of the base/standard sample. Normalizing the experimentdata to the same moisture level allows one to more accurately comparethe relative effectiveness of each contacting method at reducingacrylamide formation.

Referring back to FIG. 4, the vertical or y-axis is again labeled in ppbof acrylamide found in the finished product. The horizontal or x-axis islabeled to show the parameters of each data point. In FIG. 4, each datapoint shows a pair of vertical bars, the bars on the left of a pair areimported from FIG. 3 while the bars on the right of a pair reflect theexpected results of the same contacting process parameters if the finalproduct were fried to a uniform or standardized moisture level of 1.32%.

Once again, the first data point 41 is the base sample involving a twoto three minute water wash at ambient temperature. The second data point42 involves the contacting step according to the present invention,where the potato slices are contacted with an aqueous solutioncomprising water at a temperature of about 38° C. (100° F.) for a tenminute contact time. The left-hand bar again reflects that suchcontacting followed by frying at approximately 178° C. (353° F.) forabout 120-130 seconds will result in just over 200 ppb acrylamide in thefinished product and a finished product having a moisture level of lessthan 1%. However, the right-hand bar demonstrates that if a chip thuscontacted were fried to a standardized moisture level of 1.32%, theprojected acrylamide level would drop to approximately 150 ppb.

A similar desirable result occurs with regard to the third data point43, while the fourth data point 44 reflects that the reduction of themoisture level of the finished product slightly raises the acrylamidelevel found. Interestingly, the last data point 45 reflects significantacrylamide reduction when an aqueous solution comprising 1% L-Cysteineand a fifteen-minute contact time is used. Furthermore, a particularlylow acrylamide level is projected for a final chip moisture level of1.32% by weight. It is also interesting to note that the projectedacrylamide level for potato slices contacted with 1% L-Cysteine for afifteen-minute contact time is nearly the same as the projected levelfor slices contacted with an aqueous solution comprising water for tenminutes at about 38° C. (100° F.).

According to other embodiments, contacting the potato slices with anaqueous solution further comprises removing one or more acrylamideprecursors, such as asparagine or reducing sugars, from the raw potatoslices by leaching such acrylamide precursors out of the raw potatoslices with a potato extract or a leaching stream. Leaching ofcomponents in the potato slices by the potato extract or the leachingstream occurs for those components for which a concentration gradientexists between the potato slices and the potato extract or the leachingstream. The leaching may be accomplished selectively by a potato extractsolution that is deficient in the acrylamide precursor to be removed,but has concentration levels of other soluble matter that are at or nearequilibrium with the corresponding concentration levels in the potatoslices. The leaching may also be accomplished non-selectively by aleaching stream such as pure water. An example of selective leachinginvolves making the potato extract deficient in asparagine, and thencontacting the raw potato slices with the asparagine-deficient potatoextract to leach asparagine out of the raw potato slices. According toone embodiment, the potato extract deficient in one or more acrylamideprecursors contacts the raw potato slices in a counter-current fashion,which may lead to more effective leaching than a parallel flow. Inanother embodiment, the leaching is further enhanced by ultrasonicallyvibrating the potato extract while it is in contact with the potatoslices. If desired, the potato extract or the leaching stream can betreated to remove the leached acrylamide precursors so that the potatoextract or the leaching stream can be recycled for continuous use in theleaching of more potato slices.

One point that must be kept in mind when reviewing the effects ofmanipulating various parameters of unit operations, such as thoseeffects shown in FIGS. 3 and 4, is that all of these adjustments willhave some collateral effect on the quality and characteristics of thefinal product. Consequently, any adjustments made in any of the unitoperations must be carefully selected in order to arrive at the productexhibiting the desired final characteristics. These characteristicsinclude color, flavor, mouth-feel, density, smell, and the shelf-lifeaspects of the finished product.

FIG. 5 focuses on another aspect of unit operations and shows the effectof decreasing moisture level in the chip during the cooking stage.Referring back to FIG. 2, the cooking step 24 is a unit operation thattypically involves cooking sliced potato chips in a continuous oil fryerat high temperatures. Returning to FIG. 5, the graph thereon reflects onthe horizontal or x-axis the moisture level of the final chip product.The vertical or y-axis is again labeled in ppb of acrylamide (“AA”)found in the final product. A number of data points are then plottedshowing a percent moisture versus the acrylamide level of the finalchip. Two different frying temperatures were used with diamond symbolsrepresenting chips fried at about 178° C. (353° F.) while square symbolsare used to represent data points for chips fried at about 149° C. (300°F.). The line plots 51, 52 are curve-fitted to the data points in orderto establish a trend. The curve-fitted line plots 51, 52 follow thegeneral equation: y=c x ^(b), where “y” represents the acrylamide level,“c” is a constant, “x” is the moisture level, and “b” is the exponent of“x.” The first line plot 51 relates to the 149° C. (300° F.) fryingtemperature data points. The second line 52 relates to the data pointsplotted for the 178° C. (353° F.) frying temperature. As can be seen inFIG. 5, acrylamide levels remain very low at chip moisture levels aboveabout 3% moisture by weight regardless of frying temperature.

Whereas FIG. 5 shows the relationship between acrylamide levels andmoisture content in fried potato slices, FIG. 6 depicts the samerelationship in baked potato chip products made from a dry mix. Thevertical axis of the graph in FIG. 6 shows acrylamide concentrations,while the horizontal axis shows moisture levels by weight. While theacrylamide concentrations tend to be higher in baked potato chipproducts than in fried potato slices, FIGS. 5 and 6 both show that theacrylamide concentrations remain fairly low in cooking potato productsuntil the moisture level falls below about 3%.

What is made apparent by FIGS. 5 and 6 is that acrylamide levels inpotato chips cooked in a typical fryer increase rather dramatically oncethe moisture level falls below 3% moisture by weight, at which point itseems there is not enough moisture left to keep the product temperaturebelow an acrylamide formation temperature. For example, FIG. 5illustrates that the level of acrylamide found in the final product isrelatively low when the moisture level of the chip during the cookingunit operation is 3% by weight or greater, regardless of the exposure tohigh-temperature cooking environments. FIGS. 5 and 6 demonstrate thatmoisture level is a useful additional parameter in a unit operation thatcan be adjusted for the reduction of acrylamide formation in the finalproduct.

Unfortunately, the moisture level in a finished potato chip shouldideally be below about 2%, and preferably between about 1.3 and 1.4%.Anything higher than 2%, and even higher than 1.4% can lead to stalingand microbial spoilage issues in the packaged product, as well asorganoleptic consequences, for example, taste, texture, etc. However,changes in color, taste, and consistency of the final product can beadjusted by various means. In addition, it may be possible to counterthe consequences of finishing the food product with a higher moisturecontent by adjusting various factors in the pre-packaging step, such asextending fryer hoods, covering conveyors to the packaging machine,dehumidification of the plant environment, and various factors in thepackaging, such as packaging materials, films, bags and seals. Thus,according to another embodiment of the disclosed method for reducingacrylamide formation in thermally processed foods, a further unitoperation comprises finishing the food product as it emerges from itsfinal cooking step at a moisture content, for example, at about 1.4% byweight, about 1.6% by weight, about 1.8% by weight and about 2% byweight, or at any % moisture weight between 1.4% and 2%.

However, it is important to note that other potato products have beenknown to form significant amounts of acrylamide even at relatively highmoisture content. For example, french fries, which typically leave afryer with over 15% moisture by weight, have been shown to developsignificant amounts of acrylamide during cooking. This suggests thatacrylamide formation depends on the temperature (particularly thesurface temperature) of a cooking product rather than overall moisturecontent. In fact, studies have shown that acrylamide does not form insignificant amounts until the necessary reactants are exposed totemperatures of about 250° F./120° C. It thus appears that a potatoproduct containing acrylamide precursor compounds will not formsignificant amounts of acrylamide until, upon cooking, the producttemperature, which may differ significantly from the cooking medium'stemperature, rises above about 120° C. (250° F.). Nevertheless, themoisture content of such product can be a good indication of whether theproduct temperature has risen above a formation temperature foracrylamide.

It has been theorized by those of ordinary skill in the art thatmoisture in the product helps keep the internal product temperaturebelow the acrylamide formation temperature, even while in a relativelyhigh-temperature environment. When most of the moisture is removed,however, high-temperature surroundings can cause the product temperatureto rise above the acrylamide formation temperature. It is important tokeep in mind, though, that not all portions of a cooking product sharethe same internal temperature. French fries, for example, can be fairlythick when compared to potato slices and thus tend to have a largermoisture gradient between the inner and outer portions of the product.Consequently, it is possible for a french fry being cooked to have afairly high surface temperature even though its interior moisturecontent is high. In contrast, a potato slice is thinner and tends tohave more consistent moisture levels throughout the slice duringcooking. Thus, at least for thin products such as potato slices orfabricated potato pieces, moisture level can still be a good gauge ofits internal temperature. This also holds true for non-potato productsmade from corn, barley, wheat, rye, rice, oats, millet, and otherstarch-based grains. Furthermore, continuous cooking equipment can bedesigned with different temperature stages that progressively decreasefrom higher to lower temperatures as the moisture content of the cookingproduct decreases. This enables moisture to be removed rapidly withoutallowing the product temperature to rise above the acrylamide formationtemperature.

Consequently, one element of this invention involves dividing thecooking unit operation (the fourth unit operation 24 shown in FIG. 2)into at least two separate heating steps. A first heating step occurs atelevated temperatures to reduce the moisture level to some point nearbut above 3% by weight. The product is then finished to the desiredmoisture level of about 1-2% by weight, but preferably about 1.4% byweight, with a lower-temperature cooking step having a temperature belowabout 120° C. (250° F.). However, the process modifications describedherein are not limited to prior art processes for cooking potato slicessuch as the one disclosed in FIG. 2. These modifications are alsoapplicable in processes for making fabricated products derived frompotato, corn, wheat, rye, rice, oats, millet, and other starch-basedgrains. For example, these process modifications can be used to reduceacrylamide formation in fabricated potato and corn products, cereals,cookies, crackers, hard pretzels, and breads, to name a few. Note thatthe terms “modified cooking step” and “modified cooking unit operation”are meant to include not only FIG. 2's prior art method for cookingpotato slices but also prior art methods for preparing other foodproducts in which it is desirable to reduce acrylamide formation. Inaddition, the term “potato-based pieces” is meant to include both rawpotato slices and fabricated potato pieces derived from potato starch ordough.

Each heating step can be accomplished using various heating methods. Forexample, the first heating step can comprise atmospheric frying, vacuumfrying, microwave-assisted frying, or baking. The first heating step,however, can alternatively comprise any other method for cooking theproduct and lowering its moisture level with primary consideration givento production efficiencies such as residence time, energy costs,equipment capital costs and available floor space. When the firstheating step involves frying the product, the first heating step isoften called “par-frying,” as such frying only partially cooks theproduct until its moisture content is lowered to some point near butabove 3% by weight. The second heating step can comprise vacuum frying,low temperature oven drying, vacuum oven drying, or any method ofcooking that maintains cooking temperatures required by the secondheating step. However, other methods can also be used to reduce moisturecontent while avoiding the low-moisture/high-temperature conditions mostfavorable to acrylamide formation as long as the product temperatureremains below the acrylamide formation temperature of about 120° C.(250° F.). The second heating step is often called “finish-frying” or“finish-drying,” as the moisture content is further reduced to the finaldesired level.

By modifying the washing step 23 and/or the cooking step 24 of theprocess for making potato chips shown in FIG. 2, acrylamide levels inthe final product can be reduced significantly without adverselyaffecting product quality and final characteristics. In one preferredembodiment, a potato-chip-making process using fresh chipping potatoescombines traditional peeling, slicing, and washing steps with a modifiedcooking unit operation involving par-frying at about 165 to about 182°C. (330-360° F.) for about 1-3 minutes, followed by oven-drying belowabout 120° C. (250° F.) until the chip moisture level is reduced toabout 1.4% by weight. In tests using this preferred embodiment,acrylamide levels below 130 ppb are achieved. This preferred embodimentachieves a balance between a high level of acrylamide reduction with anacceptable change in product quality associated with the necessaryprocess modifications. However, other embodiments are possible. FIGS. 7a, 7 b, and 8 show various examples of combinations of washingmodifications comprising contacting with an aqueous solution and cookingmodifications that reduce final acrylamide levels from those levelsresulting from the prior art methods. For example, a final acrylamidelevel of more than 300 ppb is reduced to less than 100 ppb. AlthoughFIGS. 7 a, 7 b, and 8 involve embodiments for processing raw potatoslices, the modified washing methods used in those embodiments can alsoapply to other types of raw foods in which acrylamide reduction isdesirable, such as sweet potatoes, yams, and plantains. Likewise, thecooking modifications used in those embodiments can also apply to otherfried food products such as fried tortillas, fried plantains, friedsweet potatoes, and fried yams.

FIG. 7 a depicts the resulting acrylamide levels of potato chips madefrom combining several different embodiments of a modified washing stepcomprising contacting with one particular embodiment of a modifiedcooking step. The modified cooking step of FIG. 7 a comprises partiallyfrying (“par frying”) potato slices at about 178° C. (353° F.) forapproximately one to three minutes in a first heating step, thenoven-drying the potato slices at about 120° C. (250° F.) until themoisture content is reduced to approximately 1.3% by weight in a secondheating step. The advantage of par-frying followed by oven-drying isthat the low-moisture/high-temperature conditions most favorable toacrylamide formation can be avoided while still producing final productsthat are organoleptically similar to traditionally fried products.However, extensive oven-drying can give the product a dry-mouth feel andmay cause product scorching that is difficult to mask.

The vertical or y-axis of the graph in FIG. 7 a shows acrylamideconcentrations in ppb, while the horizontal or x-axis is labeled to showthe parameters of each embodiment of the modified washing stepcomprising contacting the potato slices with an aqueous solution. Eachdata point shows a pair of vertical bars: the left bar representsacrylamide concentrations after contacting and par-frying while theright bar represents acrylamide concentrations after oven-drying.Reading left to right, the first data point 71 of FIG. 7 a, like that ofFIGS. 3 and 4, is a base sample involving a two to three minute waterwash at ambient temperature, after which the sample is thenatmospherically fried to roughly 1.3% moisture by weight. The seconddata point 72 is like the first except the sample is fried to about 1.0%moisture. Note that the first and second samples 71, 72 developed about320 ppb and 630 ppb of acrylamide, respectively. The third data point 73involves the same two to three minute ambient water wash, but the sampleis then par fried to slightly above 3% moisture and oven-dried to about1.3% moisture. The left and right bars show that the sample exited thepar-frying step with a relatively low acrylamide concentration of about65 ppb and gained less than 15 ppb in the oven-drying step. The fourthdata point 74 involves an aqueous solution comprising water contactingthe potato slices for a five minute contact time at about 60° C. (140°F.), followed by the par-frying and oven-drying steps of the modifiedcooking unit operation. This five-minute, 60° C. (140° F.) contactcombined with the par-frying and oven-drying steps resulted in an evenlower final acrylamide concentration of less than 40 ppb.

The samples contacted with calcium chloride solutions 75, 76, 77 allproduced acrylamide levels higher than that produced by the sample 74contacted with pure water for five minutes at about 60° C. (140° F.).However, the final acrylamide levels of all such samples were stillbelow 80 ppb, which is significantly lower than the 320 ppb in the basesample.

The last data point 78 involves a 15-minute contact with an aqueoussolution comprising 1% L-cysteine. Interestingly, of the severalcontacting methods shown in FIG. 7 a, this contacting method producedthe lowest concentration of acrylamide. This contacting method, however,also required the longest contact time of the various methods shown inFIG. 7 a. Although using 1% L-cysteine 78 as the aqueous solution forcontacting resulted in the lowest level of acrylamide in the finalproduct, other factors must be considered, such as the effect of such along contact time on product quality, as well as the expense ofincreasing contact time.

FIG. 7 b shows the last six data points 73, 74, 75, 76, 77, 78 of FIG. 7a on a graph with a narrower acrylamide concentration scale.

In FIG. 8, the results shown in FIG. 7 b have been normalized to depictthe acrylamide levels that could be expected if the test samples werefried to a moisture level slightly above 3% by weight and thenoven-dried at about 120° C. (250° F.) to a standardized moisture levelof about 1.3% by weight. The acrylamide levels are normalized in thesame manner described above with respect to FIG. 4. When comparing theresults 83, 84, 88 shown in FIG. 8 with those of similar experiments 41,43, 45 shown in FIG. 4, one can see that dividing the cooking unitoperation into a first high-temperature heating step and a secondlower-temperature heating step significantly reduces acrylamide levels.Whereas FIG. 4 shows that frying in a traditional manner to astandardized 1.32% moisture level by weight should result in acrylamideconcentrations ranging from slightly above 100 ppb to over 400 ppb, FIG.8 shows that par-frying and oven-drying to the same standardizedmoisture level should result in significantly lower acrylamideconcentrations under 100 ppb. The cumulative benefit of combining both amodified washing unit operation comprising a contacting step with amodified cooking unit operation is particularly apparent when comparingthe 54° C. (130° F.)/5 min contact data point 43 of FIG. 4 and the 60°C. (140° F.)/5 minute contact data point 84 of FIG. 8 with the base datapoint 41 of FIG. 4. As discussed above with respect to FIG. 4,increasing the contacting time from 2-3 minutes to 5 minutes andincreasing the contacting temperature from ambient to about 54° C. (130°F.) causes the acrylamide level in the final product to decrease fromabout 330 ppb to approximately 230 ppb. The second data point 84 of FIG.8 shows that the final acrylamide level can be further reduced to lessthan 40 ppb when a similar 5-minute, 60° C. (140° F.) contacting step isfollowed by a modified cooking unit operation involving par-frying andoven-drying.

FIG. 9 shows the dramatic increase in final acrylamide concentrationsthat results from using an oven-drying temperature above about 120° C.(250° F.). In FIG. 9, the test samples were contacted and then par-friedin the same manner as in FIG. 7 b, but the samples were then oven-driedat about 176° C. (350° F.) rather than about 120° C. (250° F.). Thefinal acrylamide concentrations of the test samples were then normalizedto show the expected acrylamide levels upon reaching 0.76% by weight(which is the final moisture content that was reached in thebase-point/standard two-to-three minute water wash shown as the firstdata point). Comparing the second data point 74 of FIG. 7 b with thesecond data point 94 of FIG. 9, for example, increasing the oven-dryingtemperature from about 120° C. (250° F.) to about 176° C. (350° F.)increased the acrylamide concentration from slightly below 40 ppb toapproximately 270 ppb. This oven-drying temperature increase similarlycaused the acrylamide concentrations of the other test samples todramatically increase from below 100 ppb to over 500 ppb. Another testsample (not shown) was washed to remove surface starch, par-fried atabout 176° C. (350° F.) to a moisture content of between about 3-5% byweight, and then dried in a commercial Wenger oven at about 132° C.(270° F.) to a final moisture content of about 1.3% by weight, resultingin an acrylamide level of about 270 ppb. The results 93, 94, 95, 96, 97,98 shown in FIG. 9, as well as the results from the test sampleoven-dried at about 132° C. (270° F.), thus illustrate the advantages ofkeeping the cooking and/or drying temperature of the product less thanor equal to about 120° C. (250° F.) when the moisture content fallsbelow approximately 3% by weight. This principle applies not only to rawpotato slices but also to other raw foods, such as yams and plantains,and fabricated products derived from potato, corn, barley, wheat, rye,rice, oats, millet, and other starch-based grains.

FIG. 10 charts the results and operating conditions of yet anotherembodiment in which potato slices were washed, par-fried, and thenoven-dried. A control sample 101 was processed in a manner similar tothat described with respect to the base samples 71, 72 shown in FIG. 7a. After about a 20-30 second ambient-temperature water wash, followedby briefly contacting the potato slices with a dilute (3-5%) solution ofsodium chloride for a few seconds, a control sample 101 of 1.45 mm thickslices of peeled Hermes chipping potatoes was par-fried in oil having aninitial temperature of about 179° C. (354° F.) for approximately threeminutes to 1.4% moisture by weight. The control sample 101 had anacrylamide concentration of 640 ppb, similar to the 630 ppb produced inthe second base sample 72 shown in FIG. 7 a. The test sample 102 wassimilarly washed and contacted like the control sample 101. Using alarge commercial fryer, the test sample 102 was then par-fried in oilhaving an initial temperature of about 174° C. (345° F.) for about threeminutes until the moisture content decreased to 2.5% by weight. Thepar-fried test sample 102 was then finish-dried for about six minutesusing an oven at about 110° C. (230° F.) until the moisture leveldecreased to 1.4% by weight. Cooking in this manner produced productwith a reduced acrylamide concentration of 160 ppb, which is roughly 25%of the acrylamide concentration of the control sample 101.

In yet another set of tests (not shown) similar to those shown in FIG.10, potato slices underwent a standard wash procedure, were par-fried toabout 3-5% moisture by weight, and then oven-dried to less than about 2%moisture by weight. A control sample was washed and then fried at about179° C. (354° F.) to a finished moisture content of about 1.3% byweight, resulting in an acrylamide level of 380 ppb. However, par-fryingtest samples at about 179° C. (354° F.) to a moisture content of betweenabout 3 to about 5% resulted in acrylamide levels of approximately 64ppb. The par-fried product was then dried in a commercial Wenger oven atvarious temperatures. It was shown that drying the par-fried slices atabout 115° C. (240° F.) to a final moisture content of about 1.3%moisture by weight in a Wenger oven resulted in acrylamide levels of 125ppb. Interestingly, drying the par-fried slices at about 100° C. (212°F.) and under atmospheric or slightly less than atmospheric pressure(13.6 to 14.6 psia), even for extended periods of time (even as long as10-15 minutes), did not increase the acrylamide levels. This embodimentdemonstrates that potato slices can be par-fried at about 179° C. (354°F.) to a moisture content of between 3-5% and then oven-dried at about100° C. (212° F.) under atmospheric or slightly below atmosphericpressure without increasing the acrylamide levels beyond what is formedin the par-frying operation. To further reduce the concentration ofacrylamide formed in the cooked product, potato slices can be removedfrom the par-fry step with moisture levels as high as 10% by weight, butremoving the product too soon can affect the final texture of theproduct. Note, however, that this method is not limited to raw potatoslices and can be applied to other fried food products such as friedtortillas, fried plantains, fried sweet potatoes, and fried yams. Theadvantage of par-frying and then oven-drying at about 100° C. (212° F.)is that the cooking unit operation alone can be modified tosignificantly reduce acrylamide formation from above 300 ppb to lessthan about 70 ppb; the standard peeling, slicing, and washing steps neednot be modified.

In the set of embodiments involving par-frying followed by oven-drying,it is also possible to conduct the oven-drying under vacuum in order toenhance moisture removal. By oven-drying under vacuum, less time isrequired to dry the product to the desired final moisture content.Although it has been shown that oven-drying at or near 100° C. (212° F.)does not cause any measurable increase in acrylamide levels, oven-dryingat that temperature takes a relatively long time to dry the product.Thus, vacuum oven-drying helps decrease the amount of time it takes forproduct to dry. It also helps decrease the amount of time the product isexposed to acrylamide-forming temperatures, should higher oven-dryingtemperatures be used.

While FIGS. 7 a, 7 b, 8, and 10 depicted test results from combining oneparticular embodiment of a modified cooking unit operation with severaldifferent embodiments of a modified washing unit operation comprising acontacting step, other embodiments and combinations are possible. Forexample, the various different contacting steps shown in those figurescan instead be followed by a different modified cooking unit operation.Alternatively, an improved method for reducing acrylamide formation cansimply utilize a modified cooking unit operation without modifying anyof the other unit operations. In another set of embodiments of theinvention, the second of the two heating steps of a modified cookingunit operation comprises vacuum finish-frying rather than atmosphericfrying. By finish-frying under vacuum, the partially fried or cookedproduct emerging from the first heating step can continue to be fried,but at a temperature too low to form significant amounts of acrylamide.According to one embodiment, the vacuum pressure should be such thatfrying occurs below about 120° C. (250° F.). Such vacuum finish-fryingcan also be applied to other fried food products such as those derivedfrom potato, corn masa, barley, wheat, rice, oats, millet, and otherstarch-based grains.

FIG. 11 charts the results and operating conditions of several examplesof a modified cooking unit operation involving par-frying followed byvacuum finish-frying. In the control 110 and test samples 111, 112, 113,114, Hermes variety of chipping potatoes were peeled, sliced to about1.35 mm thickness, and subjected to a standard 20-to-30-secondambient-temperature water wash. After washing, the control sample 110was fried at atmospheric pressure in oil having an initial temperatureof about 177° C. (351° F.) for about 2.5 minutes to a moisture level of0.83% by weight, producing an acrylamide concentration of 370 ppb. InTests 1-4, all of the test samples 111, 112, 113, 114 were atmosphericpar-fried at about 177° C. (351° F.) and vacuum finish-fried at about120° C. (248° F.) and 100 millibars, but each was par-fried and vacuumfinish-fried for different lengths of time. In Test 1 111, 220 ppb ofacrylamide were found in the test sample after washing, atmosphericpar-frying for about 100 seconds to 3% moisture by weight, and vacuumfinish-frying for 44 seconds to about 0.7% moisture by weight. Theresults of Tests 2-4 112, 113, 114 show that acrylamide levels in thefinal product dramatically decrease when par-frying is stopped, andvacuum finish-drying is commenced, before the moisture content decreasesto 3% by weight. Tests 2-4 112, 113, 114 all produced final acrylamideconcentrations below 50 ppb. In Test 4 114, an acrylamide level of only13 ppb was achieved by par-frying to 10% moisture by weight, thenvacuum-frying to about 1% moisture by weight. As can be seen from thedata, partially frying slices to higher moisture content before they arelow-temperature vacuum finish-fried dramatically lowers final acrylamideconcentrations. This method can also be used to reduce the finalacrylamide concentrations in other fried products such as friedtortillas, fried plantains, fried sweet potatoes, and fried yams. Theadvantages of vacuum finish-frying after par-frying to about 3-10%moisture by weight are that the final stages of cooking can be completedat low temperatures without affecting product texture, and itseffectiveness at reducing acrylamide formation can eliminate the needfor a modified washing step comprising contacting the product with anaqueous solution. However, vacuum finish-frying also allows for thefinal stages of cooking to be completed at temperatures higher thanthose that can be used when not frying under a vacuum, while stillproviding a reduced acrylamide concentration in the finished product. Itis noted that the vacuum finish-fried product had a lighter color thanthe control sample, and transferring cooking product from the par-fryingoperation to the vacuum finish-frying unit at higher moisture levels mayimpart a bland flavor to the product. It should be kept in mind that thecapital cost of vacuum finish-frying equipment may be greater than thatof oven-drying equipment.

Similarly, vacuum par-frying can be used in the first of the two heatingsteps of a modified cooking unit operation. As an example, oneembodiment of a modified cooking unit operation involves vacuumpar-frying to a moisture content near but above the threshold moisturelevel of 3-4% by weight, then oven-drying at no greater than about 120°C. (250° F.) to completion. By par-frying under vacuum, the product canbe fried at lower temperature, thus producing less acrylamide.Furthermore, oven-drying at or below about 120° C. (250° F.) ensuresthat little to no additional acrylamide is formed during the oven-dryingstage. The advantage of using vacuum par-frying in the first of the twoheating steps, particularly when doing so below about 120° C. (250° F.)and even below about 140° C. (284° F.) when under vacuum, is that littleto no acrylamide will be formed in the first step, whereas par-fryinggenerally produces at least some level of acrylamide. However,vacuum-frying in the first heating step may create product withdifferent finished characteristics.

For baked product lines, which can involve fabricated snacks or productssuch as cereals, cookies, crackers, hard pretzels, and bread, anotherembodiment of the invention comprises a modified cooking unit operationwith a higher-temperature first baking step and a lower-temperaturesecond baking step. In the cooking unit operation of this embodiment,the product is first baked at higher temperature (above about 120° C.(250° F.)) until its moisture content is reduced to about 4% to about10% by weight. The product is then oven-dried (finish-dried or baked) ata temperature no greater than about 120° C. (250° F.) until the desiredmoisture level, typically about 1% to about 3% by weight, is attained.For example, a convection oven can be used in the higher-temperaturefirst heating step to reduce product moisture content to about 10% byweight. The oven may be divided into four heating zones in which thetemperature is highest in the first zone and gradually decreases throughthe remaining three zones. A downdraft, single zone, convection oven maybe used in the lower-temperature second heating step to complete thecooking process. Other types of ovens, however, can be used for the twoheating steps of this embodiment. Also, the lower-temperature secondheating step of this particular embodiment, like that of the embodimentsinvolving par-frying followed by oven-drying, can be performed at about0° C. (212° F.) and slightly below atmospheric pressure so that littleto no additional acrylamide is formed after the higher-temperature firstheating step.

In tests using one example embodiment that involved a higher-temperaturefirst baking step and a lower-temperature second baking step, fabricatedpotato pieces were first baked at a temperature above about 120° C.(250° F.) until the moisture levels decreased to approximately 10% byweight. The pieces were then finished at about 110° C. (230° F.) forabout 10 minutes until the moisture content decreased to about 1.7-2.2%by weight. Final acrylamide levels of about 100-200 ppb were reported.However, when several samples of partially-baked pieces werefinish-dried at about 120° C. (250° F.) to about 1.6% moisture byweight, acrylamide levels of between 470 and 750 ppb were reported.Furthermore, substantially higher acrylamide levels of between 460 and1900 ppb were produced when samples of partially-baked slices werefinish-fried at about 132° C. (270° F.) to about 1.6-2.2% moisture byweight. These results reemphasize the importance of keeping the cookingor drying temperature of a cooking product at or below about 120° C.(250° F.) during the final stages of cooking. This principle applies notonly to the cooking of fabricated potato pieces but also to otherfabricated products derived from potato, corn, barley, wheat, rye, rice,oats, millet, and other starch-based grains. This principle also appliesto the cooking of raw foods such as yams and plantains.

In another embodiment of the invention, rather than dividing themodified cooking unit operation into a higher-temperature first heatingstep and a lower-temperature second heating step, the modified cookingunit operation instead comprises vacuum frying for the entire cookingprocess. FIG. 12 charts the results and operating conditions of severalexamples of such an embodiment. In Tests 1-4 121, 122, 123, 124, variouscontrol groups of peeled, sliced, 1.45 mm thick Hermes chipping potatoeswere washed in ambient-temperature water for about 30 seconds, thenprocessed through a standard continuous fryer. The fryer inlet oiltemperature was varied within the range of about 165 to about 180° C.(329-356°), and the control samples were fried for about 3-4 minutes,resulting in acrylamide levels over 300 ppb. In contrast, the testsamples in Tests 5-7 125, 126, 127 all produced acrylamideconcentrations below 60 ppb after low-temperature vacuum frying forabout 4 to about 10 minutes at temperatures ranging from about 100 toabout 140° C. (212-284° F.) and pressures ranging from about 50 to about100 millibars. As can be seen from the data, vacuum frying at reducedtemperatures dramatically reduces the amount of acrylamide formed.Furthermore, little to no acrylamide is formed when the product isvacuum-fried below a temperature of about 120° C. (250° F.) throughoutthe entire cooking process. Tests 6 and 7 126, 127, for instance, showthat vacuum frying under about 120° C. (250° F.) and at a pressure of nogreater than 100 millibars results in virtually undetectable levels(less than 5 ppb) of acrylamide. The advantage of frying under about120° C. (250° F.) is that little to no acrylamide is formed, whereashigh-temperature par-frying causes at least some acrylamide to form.However, temperatures greater than about 120° C. (250° F.) can be usedwhen vacuum frying or vacuum finish-frying is employed, while stillachieving a reduced acrylamide concentration in the finished product.For example, in test 5 125, vacuum frying at 140° C. (284° F.) produceda product with an acrylamide content of about 53 ppb. Given this result,it seems likely that vacuum finish frying or vacuum frying alone couldproduce products having less than about 100 ppb acrylamide attemperatures up to 143° C. (290° F.). It should be kept in mind,however, that vacuum frying throughout the entire cooking process maysignificantly alter product texture, appearance, and flavor.

For baked product lines, which can involve fabricated snacks, cerealsand other starch or dough-based products as explained above, themodified cooking unit operation can alternatively compriselow-temperature baking for the entire cooking process. Low-temperaturebaking can be performed at or below about 120° C. (250° F.) so thatlittle to no acrylamide is formed. However, lower-temperature baking maycreate lighter-colored products, while higher-temperature baking maycreate darker-colored products. Thus, the applicability oflow-temperature baking depends in part on the desired colorcharacteristics of the final product.

This invention contemplates combining the teachings herein with regardto various unit operation manipulations in order to achieve a desiredacrylamide level in the end product along with the desired end-productcharacteristics. The combinations used depend on the starting productand the desired end product and can be adjusted by one skilled in theart pursuant to the teachings herein. The effect of pH on acrylamideformation is another factor that may be considered and combined with theteachings herein.

It should be understood that changes in the characteristics of the finalproduct, such as changes in color, taste, and consistency can beadjusted by various means. For example, color characteristics in potatochips can be adjusted by controlling the amount of sugars in thestarting product. Some flavor characteristics can be changed by theaddition of various flavoring agents to the end product. The physicaltexture of the product can be adjusted by, for example, the addition ofleavening agents or various emulsifiers.

While the invention has been particularly shown and described withreference to one or more embodiments, it will be understood by thoseskilled in the art that various approaches to the reduction ofacrylamide in thermally processed foods may be made without departingfrom the spirit and scope of this invention. For example, while theprocess has been disclosed herein with regard to potato products, theprocess can also be used in processing of food products made from corn,barley, wheat, rye, rice, oats, millet, and other starch-based grains.In addition to potato chips, the invention can be used in making cornchips and other types of snack chips, as well as in cereals, cookies,crackers, hard pretzels, breads and rolls, and the breading for breadedmeats. In each of these foods, the present invention's method formanipulating one or more unit operations can be combined with otherstrategies for the reduction of acrylamide to produce an acceptableacrylamide level without adversely affecting the taste, color, odor, orother characteristics of an individual food.

We claim:
 1. A method for reducing acrylamide formation in thermallyprocessed foods, said method comprising the steps of: a) providing aplurality of raw potato slices having an initial moisture level prior tocooking of at least 4% by weight; b) heating said raw potato slices to aproduct temperature above about 120° C. until said raw potato sliceshave a par-cooked moisture level ranging from about 3% by weight toabout 10% by weight, thereby forming a plurality of par-cooked potatoslices; and c) cooking said par-cooked potato slices at a producttemperature of less than about 120° C. until said par-cooked potatoslices have a final moisture level ranging from about 1% by weight toabout 2% by weight, thereby forming a plurality of potato chips having areduced acrylamide concentration, wherein said cooking at less than aproduct temperature of about 120° C. occurs at ambient pressure.
 2. Themethod for reducing acrylamide formation in thermally processed foods ofclaim 1 wherein step c) further comprises cooking at a producttemperature of less than about 115° C.
 3. The method for reducingacrylamide formation in thermally processed foods of claim 1 whereinstep c) further comprises cooking at a product temperature of less thanabout 110° C.
 4. The method for reducing acrylamide formation inthermally processed foods of claim 1 wherein step c) further comprisescooking at a product temperature of less than about 104° C.
 5. Themethod for reducing acrylamide formation in thermally processed foods ofclaim 1 wherein step c) further comprises cooking at a producttemperature of about 100° C.
 6. The method for reducing acrylamideformation in thermally processed foods of claim 1 wherein said reducedacrylamide concentration is less than 200 ppb.
 7. The method forreducing acrylamide formation in thermally processed foods of claim 1wherein said reduced acrylamide concentration is less than 130 ppb. 8.The method for reducing acrylamide formation in thermally processedfoods of claim 1 wherein said heating of step b) comprises frying in aplurality of stages in which the temperature decreases from one stage tothe subsequent stage.
 9. The method for reducing acrylamide formation inthermally processed foods of claim 1 wherein said cooking of step c) isperformed in a plurality of stages, each of which heats at asuccessively lower temperature.
 10. The method for reducing acrylamideformation in thermally processed foods of claim 1 wherein said cookingof step c) comprises oven-drying.
 11. The method for reducing acrylamideformation in thermally processed foods of claim 1 wherein step a)further comprises contacting said raw potato slices with an aqueoussolution.
 12. The method for reducing acrylamide formation in thermallyprocessed foods of claim 11 wherein said contacting is performed usingwater at an ambient temperature.
 13. The method for reducing acrylamideformation in thermally processed foods of claim 11 wherein saidcontacting is performed using an aqueous solution of calcium chloride.14. The method for reducing acrylamide formation in thermally processedfoods of claim 11 wherein said contacting is performed using an aqueoussolution of L-cysteine.
 15. The method for reducing acrylamide formationin thermally processed foods of claim 11 wherein said contactingcomprises leaching at least one acrylamide precursor out of said rawpotato slices.
 16. The method for reducing acrylamide formation inthermally processed foods of claim 15 further comprising leaching atleast one acrylamide precursor out of said raw potato slices with apotato extract that is deficient in the acrylamide precursor beingleached.
 17. The method for reducing acrylamide formation in thermallyprocessed foods of claim 1 wherein step a) further comprises contactingsaid raw potato slices with an aqueous solution having a temperatureabove ambient temperature.
 18. The method for reducing acrylamideformation in thermally processed foods of claim 1 wherein cooking ofstep c) further comprises finishing said potato chips at a moisturecontent at about 1.4% by weight.
 19. The method for reducing acrylamideformation in thermally processed foods of claim 1 wherein said cookingof step c) further comprises finishing said potato chips at a moisturecontent between about 1.4% by weight and 1.6% by weight.
 20. The methodfor reducing acrylamide formation in thermally processed foods of claim1 wherein said cooking of step c) further comprises finishing saidpotato chips at a moisture content between about 1.6% by weight and 1.8%by weight.
 21. The method for reducing acrylamide formation in thermallyprocessed foods of claim 1 wherein said cooking of step c) furthercomprises finishing said potato chips at a moisture content betweenabout 1.8% by weight and 2% by weight.